Because of the height above the ground of the cab of certain agricultural vehicles, such as tractors, combine harvesters or forage harvesters, it is often necessary to provide steps leading up to the cab door. If the steps reach down to ground level, they can be negotiated easily and safely. There is however a risk of the lowermost step snagging the ground when the vehicle is driven over uneven terrain. If the lowest step is made sufficiently high to avoid such a risk, then it becomes difficult for the driver to climb onto the first step.
It has previously been proposed to provide vehicles having elevated cabs with access steps that can be moved to different positions. For example, JP 2000168453 describes a ladder that can be raised manually by pivoting it about a horizontal axis, wherein the ladder is made up of two telescopically collapsible sections.
Another ladder is described in FR 2551490. The ladder is made of two sections of which the first is pivotably secured to the vehicle and the section is slidable up and down relative to the first. An actuator that cannot be operated when the vehicle is capable of moving is used to extend and contract the ladder.
U.S. Pat. No. 1,915,327 describes a power driven step for a public service vehicle than can be raised and lowered by sliding or folding. The latter patent is concerned with the safety of such a step and provides a control to prevent the vehicle from being operated while someone is standing on the step or an object, such as clothing, is caught up in the step.
U.S. Pat. No. 6,178,364 describes steps that are used on a truck intended for use on metalled road surfaces. In this case, snagging the ground is not a problem but having laterally projecting steps is unacceptable in view of the increased vehicle width. This patent teaches a set of steps that can swivel about a vertical axis to allow them to be stacked behind the front wheel of the lorry.
In vehicles with manually operated access steps, there is a risk of the step being left in its extended position while the vehicle is moving which can result in damage to the step and in a mud build up on the step. With powered steps, there is a risk that the actuator and the mechanical linkages used to raise and lower the step can be damaged by contact with the ground or an accumulation of debris.